Piston for an internal combustion engine

ABSTRACT

A cooling structure for an internal combustion engine piston is provided. The piston includes an oil cooling channel integrated in the piston. The oil cooling channel has a bottom surface facing towards a top surface of the piston and a top surface facing away from the top surface of the piston. The oil cooling channel is provided with an oil inlet and an oil outlet which are laterally separated from each other. The bottom surface and/or the top surface of the oil cooling channel is slanted relative to a central axis of a wrist pin opening provided in said piston.

BACKGROUND AND SUMMARY

The present invention relates to a cooling structure for an internal combustion engine piston.

Cooled pistons having an oil inlet are known from example U.S. Pat. No. 3,221,718 and DE 3733964. The oil inlets used as catch funnels for cooling oil that is dispensed from an oil spraying nozzle connected with the engine housing have inners walls that are configured to be funnel shaped, cylindrical, oval or in the form of a venture jet. In order to achieve better distribution, in the cooling duct, of the oil captured in this manner, additional dividers are inserted into the wall of the cooling duct, which lie opposite the exit surface of the oil inlet.

Using such shaping structures, the result supposed to be achieved is that the oil stream that widens from the oil spraying nozzle is captured and passed to the cooling duct. These structures demonstrates defects in achieving a continuous oil fill level of the cooling duct, due to disadvanatageous flow and friction conditions during entry of the cooling oil into the inlet.

U.S. Pat. No. 7,051,684 tries to overcome the above mentioned problems and shortcomings. However, in U.S. Pat. No.7,051,684 there is still a problem with the fill level in the oil cooling duct and the amount of oil circulating in said oil cooling duct in said piston for achieve sufficient cooling of the piston. Especially, there is a problem if the oil level in the oil duct in said piston becomes to small. The small oil level may cause too much air to be mixed with the oil when the engine rev is in a higher range. Air is a very bad thermal conductor, which decreases the cooling efficiency dramatically. Another problem with the design of U.S. Pat. No. 7,051,684 is that the circulation of oil in the oil cooling duct is too low. A too low circulation of oil in the oil cooling duct will further decrease the cooling efficiency.

It is desirable to provide a cooling structure for an internal combustion piston which is more efficient compared to the conventional structures.

According to a first aspect of the invention it is provided a cooling structure for an internal combustion engine piston comprising an oil cooling channel integrated in said piston. Said oil cooling channel having a bottom surface facing towards a top surface of said piston and a top surface facing away from said top surface of the piston, said oil cooling channel is provided with an oil inlet and an oil outlet which are laterally separated from each other. Said bottom surface and/or said top surface of said oil cooling channel is slanted relative to a central axis of wrist pin opening provided in said piston.

An advantage of this aspect is that the oil flow can be better controlled resulting in improved cooling efficiency.

Another advantage is that oil may be forced from the oil inlet to the oil outlet in almost a complete rotation of a crank axle in said internal combustion engine.

In another example embodiment of the present invention said bottom surface is slanted downwards, relative to said wrist pin opening, from the oil inlet to the oil outlet.

An advantage of this embodiment is that oil is forced to the outlet automatically while the piston is moved from a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC).

In another example embodiment of the present invention said top surface is slanted upwards, relative to said wrist pin opening, from the oil inlet to the oil outlet.

An advantage of this embodiment is that oil is forced to the outlet automatically while the piston is moved from the TDC to the BDC.

In still another example embodiment of the present invention said oil outlet is provided with a mechanical stop.

An advantage of this embodiment is that the oil level can be better controlled.

In yet another example embodiment of the present invention said oil inlet is provided with a mechanical stop.

An advantage of this embodiment is that the oil circulation can be better controlled.

In another aspect of the present invention it is provided a method of cooling a piston in an internal combustion engine, comprising the steps of providing an oil cooling channel in said piston, providing oil into said oil cooling channel via an oil inlet, transferring oil from said oil inlet to an oil outlet provided in said oil channel, forcing said oil from said oil inlet to said oil outlet by a bottom surface of said oil cooling channel which is slanted relative to a central axis of a wrist pin opening provided in said piston while said piston is moving from a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC) and/or by a top surface of said oil cooling channel which is slanted in an opposite direction relative said bottom surface while said piston is moving from the TDC to the BDC.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown schematically:

FIG. 1 is a schematic cross sectional view of an example embodiment of a cooling structure for an internal combustion engine piston according to the present invention,

DETAILED DESCRIPTION

FIG. 1 depicts schematically a cross sectional view of an example embodiment according to the present invention of a cooling structure for an internal combustion engine piston 100. Said piston 100 comprising a body 101, a top surface 112, a combustion chamber cavity 114, an oil cooling channel 102, a wrist pin opening 104, an oil inlet 121, an oil inlet mechanical stop 120, an oil outlet 131, and an oil outlet mechanical stop 130.

Oil is provided to the oil cooling channel 102 in said piston by a nozzle 145 attached to an oil pump 140. The oil is injected into the oil inlet 121 in the piston from below as indicated by arrows 147 in FIG. 1. The oil pump 140 may be the same pump as used to circulate oil to the engine bearings. A separate pump 140 may also be used for injecting oil to the pistons.

The combustion chamber cavity is typical for self igniting engines such as diesel engines. However, a top portion in natural aspirated gasoline engines may very well have the opposite, i.e., instead of a cavity a dome for increasing the compression ratio. These two examples illustrates that there are numerous different design of the top portion of a piston depending on which fuel, is used and which purpose or performance one wants to optimize.

The body 101 of the piston 100 may be manufactured of any material which can resist the temperatures in the combustion chamber, mainly aluminum alloys are used for that purpose though other alloys may be seen.

In FIG. 1, the position of the wrist pin hole 104 is located below the oil cooling channel 102. The position of the wrist pin hole may vary between different piston designs and may be arranged close to the top of the piston, in the middle or closer to the bottom of the piston.

The oil cooling channel 102 is integrated in the piston 100. Said oil cooling channel 102 having a bottom surface facing towards the top surface 112 of said piston 100 and provided with an oil inlet 121 and an oil outlet 131 which are laterally separated to each other. The bottom surface of said oil cooling channel 102 is slanted relative to a central axis of a wrist pin opening 104 provided in said piston 100.

In FIG. 1 said slanted bottom surface of said oil cooling channel 102 is better understood from lines 180 and 182. Line 184 is a line representing the central axis of the piston 100. Line 182 represents a line perpendicular to said central axis 184 of the piston 100. Line 180 represents a line in parallel with the bottom surface of said oil cooling channel 102. The bottom surface is slanted downwards from the oil inlet 121 to the oil outlet 131 in FIG. 1. A slope is indicated is denoted by 108 may be in the range of 0.1-20 degrees. When the piston is moved from a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC) oil is forced to the bottom surface of the oil cooling channel and due to its slope forced from the oil inlet 121 to the oil outlet 131.

A top surface of said oil cooling channel 102 may be slanted in an opposite direction compared to the bottom surface, i.e., when the piston is moved from is moved from the TDC to the BDC oil is forced to the top surface of the oil cooling channel and due to its slope forced from the oil inlet 121 to the oil outlet 131.

In one example embodiment there is only a slope of the bottom surface of the oil cooling channel 102. In another example embodiment there is only a slope in the top surface of the oil cooling channel 102. In still another example embodiment there is a slope of the bottom surface as well as the top surface of the oil cooling channel 102. The slope of the top surface of the oil cooling channel may have a different inverse slope angle compared to the bottom surface.

The oil outlet is provided with the mechanical stop 130. This mechanical stop 130 serves to prohibit all oil from escaping from the oil cooling channel 102, i.e., the stop will make sure that there is always some oil in the oil cooling channel 102 for cooling the piston 100. By selecting a suitable slope of the bottom surface of the oil cooling channel one may optimize the cooling efficiency to ones desire.

The oil inlet 121 is also provided with a mechanical stop 120. This mechanical stop 120 has the functionality to prevent oil from escaping out of the oil inlet 121, i.e., forcing the oil to circulate from the oil inlet 121 to the oil outlet 131.

A height of the mechanical stop 130 is denoted with 110, which may be selected out of the desired performance, i.e., a higher mechanical stop will make sure that more oil is collected within the oil cooling channel at a given moment. A height of the mechanical stop 120 is denoted with 106 and a higher mechanical stop 106 may result in more oil circulating to the outlet 131 at a given moment compared to if one is using a lower mechanical stop 120. The amount of oil injected to the oil cooling channel 102 may be determined from a pump pressure and flow from the pump 140. This may be adjusted for different purposes, i.e., a higher pump pressure may be used if one wants more cooling efficiency and/or the nozzle may be exchanged to one with more flow capacity.

The cooling structure may be provided in a vehicle such as a lorry, truck, bus, personal car, wheel loader, construction equipment vehicles etc.

The invention may be applied to any internal combustion engine such as diesel engine, gasoline engine, bifuel/flexifuel engine with one or a plurality of cylinders.

The invention must not be regarded as being limited to the examples of embodiment described above, a number of further variants and modifications being feasible without departing from the scope of the following claims. 

1. A cooling structure for an internal combustion engine piston comprising an oil cooling channel integrated in the piston, the oil cooling channel having a bottom surface facing towards a top surface of the piston and a top surface facing away from the top surface of the piston, the oil cooling channel being provided with an oil inlet and an oil outlet which are laterally separated from each other, the bottom surface and/or the top surface of the oil cooling channel being slanted relative to a central axis of a wrist pin opening provided in the piston.
 2. The cooling structure according to claim 1, wherein the bottom surface is slanted downwards, relative to the wrist pin opening, from the oil inlet to the oil outlet.
 3. The cooling structure according to claim 1, wherein said the top surface is slanted upwards, relative the wrist pin opening, from the oil inlet to the oil outlet.
 4. The cooling structure according to claim 1, wherein the oil outlet is provided with a mechanical stop.
 5. The cooling structure according to claim 1, wherein the oil inlet is provided with a mechanical stop.
 6. A method of cooling a piston in an internal combustion engine, comprising the steps of providing an oil cooling channel in the piston, providing oil into the oil cooling channel via an oil inlet, transferring oil from the oil inlet to an oil outlet provided in the oil channel, forcing the oil from the oil inlet to the oil outlet by a bottom surface of the oil cooling channel which is slanted relative to a central axis of a wrist pin opening provided in the piston while the piston is moving from a Bottom Dead Centre (BDC) to a Top Dead Centre (TDC) and/or by a top surface of the oil cooling channel which is slanted in an opposite direction relative the bottom surface while the piston is moving from the TDC to the BDC. 